A guideless rear window shade for motor vehicles is described in DE 36 12 165 A1. The disclosed window shade has a rotatable supported wind-up roller shaft to which one edge of a trapezoidal shade material is attached. The other edge of the shade material that is remote from the wind-up roller shaft is connected to a pull rod or a pull-out element. This pull-out element sits on the free end of two holding levers that are supported so that they can rotate next to the wind-up roller shaft on hinge axes. The hinge axes are aligned perpendicular to the axis of the wind-up roller shaft.
Two drive devices are used to hold and retract the window shade. One drive device comprises a spring-driven motor, which is housed in the wind-up roller shaft. The wind-up roller shaft is biased in the winding direction to take up the window shade material. The other activation and drive device is a geared motor, which carries a crank disk on its output shaft. The crank disk is connected via coupling rods to the holding levers. In the retracting position, the holding levers lie parallel to the wind-up roller shaft and are moved by setting the geared motor into a position in which the holding levers stand essentially perpendicular to the wind-up roller shaft. In this way, the free ends of the holding levers slide through grooves that run along the pull-out element. The end of the holding lever undergoes a combination movement, namely a linear movement parallel to the longitudinal extent of the pull-out element and also a tilting or pivoting movement. To enable this degree of freedom, a sliding body is between the pull-out profile and the end of the holding lever, which is connected via a hinge to the holding lever. The head of the sliding body runs through the groove in the pull-out element. The groove in the pull-out element is undercut in the sense that the groove is assembled from a groove chamber and a groove slot. The width of the groove slot is smaller than the width of the groove chamber.
Because the spring-driven motor is constantly biased, the window shade material is again retracted and the window shade material exerts a tilting moment on the pull-out element, in particular a tilting moment relative to an axis that is parallel to the pull-out element and thus parallel to the wind-up roller shaft. In commercially available window shades, to transfer this tilting moment to the holding lever, the head of the sliding body has a shape similar to a T nut, while the groove chamber has a rectangular cross sectional profile.
It has been shown that after long use, the movement of the sliding body in the guide groove is not entirely smooth, but is characterized by fits and starts while being pulled out and retracted. Such movement is generally undesirable.